It would be Twojeffs' 'Always Perfect Plants' you'd be looking for:
http://www.moreawesomethanyou.com/smf/index.php?topic=2612.0. It doesn't help existing out-of-control plants, which would still have to be trimmed, but it'll prevent them from having to be trimmed again, ever. Don't know how I ever played this game without it.
(P.S. -- you really should poke around here more -- there's tons of great hacks in Pescado's, Twojeffs' and Crammyboy's forums...)